The present invention relates to a throttle valve actuating apparatus for use in an internal combustion engine such as a gasoline engine and, particularly to a throttle valve actuating apparatus suitable for use in an internal combustion engine of an automobile.
In an internal combustion engine for use in an automobile, in general a throttle valve of a throttle valve actuating apparatus is actuated through a wire member by operating an acceleration pedal. Further, when the acceleration pedal is released and the wire member has cut off, so as to close surely the throttle valve, a fail-safety function for the throttle valve is provided in the throttle valve actuating apparatus.
Namely, to provide the fail-safety function for the closing motion of the throttle valve, a return spring member is installed on the throttle valve shaft. In general, the throttle valve actuating apparatus is constituted by stepping on the acceleration pedal and the throttle valve is forced to turn toward an opening direction of the throttle valve against the elastic force through the return spring member.
Further, in the conventional throttle valve actuating apparatus techniques, in general a return spring member having at least two independent torsional coil spring members is provided on the throttle valve shaft and, consequently, even when one of the at least two independent torsional coil spring members of the return spring member is cut-off, the throttle valve is forced to an idle position and thus the throttle valve can be maintained surely.
However, when the return spring member having at least two independent torsional coil spring members is provided on the throttle valve shaft, it requires a superfluous space in the throttle valve actuating apparatus and further there is a possibility of the large space requirement for the throttle valve actuating apparatus.
Accordingly, even when the return spring member having at least two independent torsional coil spring members is provided on the throttle valve shaft, so as to constitute compactly the throttle valve actuating apparatus, the technique of the return spring member having two torsional coil spring members with different winding diameter is provided concentrically on the throttle valve shaft in the different lines is disclosed in, for example, Japanese patent publication No. 54,938/1986.
In this prior technique, two coil spring members of the return spring member are provided at an upper position and a lower position around the throttle valve shaft. The upper coil spring member has the large winding diameter and the lower coil spring member has the small winding diameter, respectively. Each of the upper and lower coil spring members of the return spring member is supported by a collar member having a collar portion (guide portion), respectively.
Further, a cylindrical shape sleeve member is provided between the upper and lower coil spring members, this sleeve member preventing the upper and lower coil spring members from contacting each other and also from interfering with each other.
Accordingly, in the above stated Japanese patent publication No. 54,938/1986, the throttle valve actuating apparatus has a complicated structure having many components and the return spring member comprises the concentrically arranged two coil spring members at the different radial directions of the throttle valve shaft.
Namely, in the technique shown in Japanese patent publication No. 54,938/1986, the return spring member is comprised of the upper coil spring member having the large diameter and the lower coil spring member having the small diameter, and on the throttle valve shaft the cylindrical shape sleeve member for determining a setting position of these coil spring members and other components for distinguishing the large diameter coil spring member and the small diameter coil spring member are provided specially.
In the above stated prior technique, however, there has not been taken fully into consideration the hysteresis phenomenon (reaction force) in the return torque which is given at the throttle valve shaft according to the return spring member, thereby causing a scattering phenomenon problem on the torque which appears to the throttle valve shaft.
As a result, when the throttle valve shaft is moved toward an opening direction of the throttle valve, the above distinguishing components contact the return spring member. In accordance with the contact between the above distinguishing components and the coil spring member, the hysteresis phenomenon is generated and the scattering phenomenon occurs on the coil spring members.
Further, the technique about a return spring member for a throttle valve actuating apparatus comprising two coil spring members is disclosed in, for example, Japanese patent laid-open No. 87,838/1989. In this latter prior art, the return spring member comprises a combination of two coil spring members having a same winding diameter and the same number of turns.
Namely, the return spring member disclosed in this prior art comprises a main coil spring member and an assist coil spring member for a fail-safety function. Each of one coil portion of the main coil spring member and the assist coil spring member are adjacently arranged. Namely, one coil portion of the assist coil spring member is inserted closely between two adjacent coil portions of the main coil spring member.
A sleeve member for retaining the return spring member is provided on a boss which is formed on bearing member portions of a throttle valve main body of the throttle valve shaft.
In the technique shown in Japanese patent laid-open No. 87,838/1989, the sleeve member for retaining the return spring member is provided on the boss formed on the throttle valve main body.
In general, the throttle valve main body is manufactured through an aluminum die casting method. For this reason between the sleeve member and the throttle valve main body a large friction resistance occurs. The return spring member is arranged on the sleeve member but is not arranged directly on the throttle valve shaft.
Further, when the throttle valve is opened gradually, the return spring member is twisted at the same time the diameter of the return spring member decreases. In particular, the coil diameter of the return spring member has the small outer diameter, and the change in the inner diameter of the return spring member increases furthermore.
Consequently, when the return spring member is turned toward the opening direction of the throttle valve, the return spring member may slip from the outer diameter portion. In this time, the force is transmitted to the sleeve member and, further this force is transmitted to the sleeve member and the throttle valve main body.
Further, when the return spring member is moved, the sleeve member is going to move, however, between the throttle valve main body and the sleeve member since the friction resistance is high via the large friction force acting thereon. Due to this large friction force the hysteresis phenomenon generated and thereby the torque may scatter.
Further in this prior technique, in addition to the above stated hysteresis phenomenon due to the return spring member, a further hysteresis phenomenon is generated as follows.
Namely, when the throttle valve is turned toward the opening direction of the throttle valve the return spring member is wound, and the inner diameter of the return spring member decreases, while at the same time the inner diameter of the return spring member is squeezed remarkably at both end portions.
Besides, in this prior technique, since the sleeve member is provided and further the return spring member is provided on an outer periphery, as a result, when the throttle valve is turned toward the opening direction the return spring member makes a tight squeeze with the sleeve member.
Since the throttle valve is turned toward the opening direction the torsional force acts on two coil spring members of the return spring member in a reversed direction, and results in the smaller size of the coil diameter portion of the return spring member.
To sum up, in Japanese patent laid-open No. 87,838/1989, since the return spring member is provided on the throttle valve main body, the large friction force acts at the mounted contacting portion of the return spring member, thereby the return spring member can not move smoothly. At the non-smooth portion of the return spring member, the return spring member can not perform the original function, thereby a torque transmitting loss of the throttle valve shaft occurs.
In the above stated latter prior technique, however, there has not been fully into consideration the hysteresis phenomenon (reaction force) in the return torque which is given at the throttle valve shaft according to the return spring member. Thereby, it has a problem that the scattering phenomenon is caused on the torque which appears at the throttle valve shaft.